1. Field of the Invention
The present invention relates to dissolution of a loop relating to a network device (such as a switch).
2. Related Art
When a network device is connected incorrectly, a loop may be generated.
FIG. 20 is diagrams showing an example of a network configuration in which a loop is generated according to prior art, and showing an example (FIG. 20(a)) of the network configuration before a loop is generated and an example (FIG. 20(b)) of the network configuration after the loop is generated.
Referring to FIG. 20(a), a port 101 of the switch 100 and a port 201 of a hub 200 are correctly connected with each other. It should be noted that the switch 100 includes ports 102 and 103 in addition to the port 101, and the hub 200 includes ports 202 and 203 in addition to the port 201.
However, referring to FIG. 20(b), the port 103 of the switch 100 and the port 203 of the hub 200 are incorrectly connected with each other. In this case, a loop is generated.
For example, a frame output (broadcasted) from the port 101 is output via the port 201 and the hub 200 from the port 203. Further, the frame output from the port 203 is output via the port 103 and the switch 100 from the port 101.
For example, a frame output (broadcasted) from the port 103 is output via the port 203 and the hub 200 from the port 201. Further, the frame output from the port 201 is output via the port 101 and the switch 100 from the port 103.
When a loop is generated in this way, a communication is interfered. It is thus known that a loop is detected by means of a loop detection frame (LDF), thereby dissolving the loop.
FIG. 21 is a diagram showing a detection principle of a loop by means of the LDF according to prior art, and shows a case in which the LDF is output from the port 101 (FIG. 21(a)), and a case in which the LDF is output from the port 103 (FIG. 21(b)).
Referring to FIG. 21(a), when the LDF is output from the port 101, the LDF is output via the port 201 and the hub 200 from the port 203. Further, the LDF output from the port 203 is received at the port 103.
Referring to FIG. 21(b), when the LDF is output from the port 103, the LDF is output via the port 203 and the hub 200 from the port 201. Further, the LDF output from the port 201 is received at the port 101.
On this occasion, while the LDF is periodically (such as at an interval of 1 second) output from the each port of the switch 100, and if the LDF is detected at any port of the switch 100, it can be determined that a loop is generated. If the switch 100 determines that a loop is generated, the loop can be dissolved by shutting off a communication on a port (at least one port of ports 101 and 103) relating to the loop generation.